Archaeological Dating Methods Cheat Sheet: A Comprehensive Guide

Introduction to Archaeological Dating

Archaeological dating methods are essential techniques used to determine the age of artifacts, sites, and contexts, allowing archaeologists to establish chronologies, understand cultural developments, and interpret past human activities. Dating methods fall into two main categories: relative dating, which determines age relationships between materials without assigning specific calendar years, and absolute dating, which provides actual calendar dates or ranges. A comprehensive understanding of these methods, their applications, and limitations is crucial for accurate archaeological interpretation and research design.

Relative Dating Methods

Stratigraphy

Best Practices:

• Record layer characteristics systematically (color, texture, composition)
• Use standardized recording systems (Harris Matrix, context sheets)
• Photograph and draw sections clearly showing relationships
• Take samples from secure contexts for absolute dating

Seriation

Statistical Approaches:

• Correspondence Analysis (CA)
• Multidimensional scaling
• Battleship curves for visualization

Typology

Implementation Steps:

1. Identify key attributes for classification
2. Establish type definitions with clear criteria
3. Place types in relative sequence using associations
4. Cross-check with absolute dating when available

Other Relative Methods

Absolute Dating Methods: Radiometric

Radiocarbon Dating (¹⁴C)

Key Considerations:

• Calibration essential to convert radiocarbon years to calendar years
• Marine reservoir effect (-400 years average offset for marine samples)
• Old wood problem (tree inner rings significantly older than death/use)
• Contamination risks (conservation treatments, handling, rootlets)

Calibration Process:

# Example R code using rcarbon package for calibration
library(rcarbon)

# Calibrate a single radiocarbon date
my_date <- calibrate(x=4500, errors=30, calCurves='intcal20', 
                     timeRange=c(5000,3000))

# Plot calibrated date
plot(my_date)

# Calibrate multiple dates
dates <- c(4500, 4200, 3900)
errors <- c(30, 35, 40)
cal_dates <- calibrate(x=dates, errors=errors, calCurves='intcal20')

# Sum probability distributions
spd <- spd(cal_dates)
plot(spd)

Potassium-Argon (K-Ar) and Argon-Argon (⁴⁰Ar/³⁹Ar)

Applications:

• Dating volcanic layers in archaeological sequences
• Establishing chronology for early hominin sites
• Dating ancient stone tool technologies

Limitations:

• Requires volcanic contexts
• Argon loss can lead to younger dates
• Excess argon can lead to older dates
• Not applicable to most archaeological materials directly

Uranium Series Dating

Applications in Archaeology:

• Cave sites with flowstone or stalagmites
• Dating fossil bones in uranium-rich environments
• Paleolithic art in caves with calcite formations

Limitations:

• Assumes closed system (no uranium/daughter loss)
• Secondary uranium uptake in bones problematic
• Complex preparation and measurement requirements

Absolute Dating Methods: Trapped Charge

Thermoluminescence (TL)

Sampling Protocol:

1. Avoid exposure to light and heat during sampling
2. Collect surrounding soil for dose rate measurement
3. Document depth and shielding conditions
4. Sample interior material (avoid surface)

Optically Stimulated Luminescence (OSL)

Applications:

• Dating sediment deposition
• Site formation processes
• Landscape evolution
• Context dating when organic materials absent

Common Issues:

• Incomplete bleaching (residual signal)
• Bioturbation mixing materials of different ages
• Heterogeneous radiation environment
• Post-depositional disturbance

Electron Spin Resonance (ESR)

Applications:

• Early hominin sites
• Pleistocene archaeological sites
• Sites with poor organic preservation

Key Considerations:

• Requires assumptions about uranium uptake history
• Sensitivity to environmental radiation
• Complex preparation and measurement

Other Absolute Dating Methods

Dendrochronology (Tree-Ring Dating)

Process:

1. Measure ring widths in sequence
2. Cross-match patterns between samples
3. Compare with master chronologies
4. Identify exact calendar years

Applications:

• Dating wooden structures, buildings, ships
• Calibration of radiocarbon dates
• Climate reconstruction
• Art history (panel paintings)

Archaeomagnetism

Requirements:

• In situ sampling of undisturbed features
• Regional archaeomagnetic calibration curve
• Measurement of both direction and intensity is ideal

Sampling Protocol:

1. Identify intact fired feature
2. Document orientation accurately
3. Take oriented samples (usually plaster caps)
4. Preserve orientation during transport

Obsidian Hydration Dating (Calibrated)

Variables Affecting Accuracy:

• Temperature history
• Humidity conditions
• Chemical composition of obsidian source
• Surface damage during burial

Calibration Approaches:

• Empirical (matched pairs with radiocarbon)
• Induced hydration experiments
• Source-specific rate development

Other Chronometric Methods

Historical/Cultural Dating Methods

Integration and Methodological Approaches

Bayesian Chronological Modeling

Core Principles:

• Combines prior information (stratigraphic relationships) with dating evidence
• Updates probability distributions based on constraints
• Provides more precise and realistic date ranges

Common Software:

• OxCal (Oxford)
• BCal (Sheffield)
• ChronoModel (CNRS)

# Example OxCal code for sequence model
Plot()
{
  Sequence("Site Phase Model")
  {
    Boundary("Start Phase 1");
    Phase("Phase 1")
    {
      R_Date("Sample A", 3500, 30);
      R_Date("Sample B", 3450, 35);
    };
    Boundary("End Phase 1/Start Phase 2");
    Phase("Phase 2")
    {
      R_Date("Sample C", 3300, 30);
      R_Date("Sample D", 3250, 40);
    };
    Boundary("End Phase 2");
  };
};

Key Benefits:

• Incorporates archaeological knowledge into chronological models
• Can identify outliers and problematic dates
• Creates more precise phase transitions and event dating
• Enforces stratigraphic constraints

Multi-Method Approaches

Best Practices:

• Cross-check multiple methods when possible
• Target different material types
• Address discrepancies systematically
• Use Bayesian modeling to integrate results

Sampling Strategies and Field Considerations

Sample Selection Guidelines

Field Documentation Requirements

Essential Field Documentation:

• Precise 3D location
• Stratigraphic relationships
• Associated materials
• Evidence of disturbance
• Depth below surface
• Photographs before removal
• Environmental conditions

For Dose Rate Measurements (OSL/TL/ESR):

• In-situ gamma spectrometry if possible
• Bulk sediment samples around specimen
• Moisture content assessment
• Depth for cosmic contribution
• Shielding conditions

Common Challenges and Solutions

Contamination Issues

Sample Selection Challenges

Calibration and Interpretation Issues

Best Practices and Reporting Standards

Research Design

• Identify key chronological questions before excavation
• Budget adequately for comprehensive dating program
• Incorporate geoarchaeological expertise
• Plan multi-method approach where possible
• Create sampling strategy before fieldwork

Documentation and Reporting

Essential Information to Report:

• Laboratory code/reference number
• Uncalibrated measurements with errors
• Calibration curve and program used
• Material dated (species identification for organics)
• Context description and associations
• Pretreatment methods
• Quality indicators (C:N ratios, % collagen, etc.)
• Any corrections applied (reservoir effects, etc.)

Data Management

• Maintain comprehensive database of all dates
• Link dates to stratigraphic database
• Update chronological models as new dates added
• Archive samples for potential future analysis
• Share data through appropriate repositories

Resources for Further Learning

Key Reference Books

• Taylor, R.E. & Bar-Yosef, O. (2014). Radiocarbon Dating: An Archaeological Perspective. Routledge.
• Aitken, M.J. (1990). Science-Based Dating in Archaeology. Longman.
• Walker, M. (2005). Quaternary Dating Methods. Wiley.
• Bronk Ramsey, C. (2017). Methods for Summarizing Radiocarbon Datasets. Radiocarbon, 59(6), 1809-1833.
• Liritzis, I. et al. (2013). Luminescence Dating in Archaeology, Anthropology, and Geoarchaeology. Springer.

Online Resources

• Oxford Radiocarbon Accelerator Unit
• IntCal Calibration Curves
• Chronological Database Tools
• International Centre for Archaeochronological Research
• Dating Service Guidelines (English Heritage)

Key Laboratories

• Oxford Radiocarbon Accelerator Unit (ORAU), UK
• Beta Analytic, USA
• Groningen Radiocarbon Laboratory, Netherlands
• SUERC, UK
• Cologne AMS Centre, Germany
• University of Arizona AMS Facility, USA
• Luminescence Dating Laboratory, University of Washington, USA
• Berkeley Geochronology Center, USA

Remember that dating methods should be selected based on the specific research questions, material availability, expected age range, and required precision. Integration of multiple methods and careful consideration of archaeological context are essential for building robust chronologies.